{PE[i,j]:0<=i<4 and 0<=j<4}
{PE[i,j]->PE[i-1,j] ; PE[i,j]->PE[i,j-1] ; PE[i,j]->PE[i+1,j-1] ; PE[i,j]->PE[i-1,j-1]}
256 1024 64 16